1. Field of the Invention
The present invention relates to a defrosting control unit for showcases suitable for concentrated control of defrosting of a plurality of showcases such as those used in retail stores and supermarkets marketing fresh grocery, fish, meat, etc. The present invention also relates to a centralized showcase defrosting system using such a defrosting control unit.
2. Description of the Prior Art
When a plurality of series of showcases are to be defrosted independently of another, it has been conventional to set up defrosting starting times for respective showcase series in advance and to start defrosting at the respective defrosting starting times. Defrosting starting times were selected to be in the nighttime when no or few customers were expected to be present in the store so that the defrosting would impose a minimum of inconvenience on the customers.
During continued cooling, flow of cool air tends to be blocked due to settling of frost on an evaporator portion of a cooling apparatus. This phenomenon is called clogging. Defrosting is carried out in order to avoid the occurrence of clogging.
The conventional defrosting method, however, suffers from limitations on the time interval for defrosting because of the performance of the showcase, and hence defrosting must be done at least once during the daytime when many customers are shopping in the store. Defrosting results an increase in the temperature of the showcase, and this spoils the purchasing volition of customers who want to get goods as fresh as possible.
Conventionally, the time interval for defrosting has been set up rather short for safety. As a consequence, defrosting will start even if only a small amount of frost has settled on the evaporator when the set-up time is reached. Therefore, problems arise in that the freshness of goods decreases rapidly due to an unnecessary increase in the temperature in the showcase, and in that power is consumed by a heated excessively or in vain.